Anemia can induce frequent bouts of stress erythropoiesis as accelerated red blood cell production. In chronic disease settings, these bouts often become compromised. Clinically, recombinant human erythropoietin (EPO) and erythropoiesis stimulating agents (ESAs) are used to enhance red cell production during anemia, but are associated with adverse hypertensive and thrombotic effects. New in-roads to anemia therapy, therefore, stand to be advanced via an improved understanding of factors required for stress erythropoiesis. The Wojchowski laboratory identified Trib3 pseudokinase as a major EPO/Jak2/STAT5 target gene in erythroid lineage cells, and has established a Trib3-knockout (Trib3-KO) mouse model to investigate Trib3's erythropoietic roles. In Trib3-KO mice, I have found that steady state erythropoiesis is unperturbed, but during anemia or ESA administration stress erythropoiesis in bone marrow is compromised. To our knowledge, Trib3 is the first identified factor that acts specifically during medullary stress erythropoiesis. Trib3, ad its erythroid expression, is highly conserved from mice to humans, hence, studies in mice should also inform on human stress erythropoiesis. To investigate Trib3's specific erythropoietic activity, SPECIFIC AIM 1 will first define functional roles for Trib3 in medullary erythroid progenitor cell formation during metabolic stress, and during stress erythropoiesis induced by anemia. Here I will assess Trib3's roles as an effector of the unfolded protein response as induced by leucine or glucose limitation, and during sustained EPO administration. I will also investigate Trib3's effects on medullary stress erythropoiesis in vivo during the anemia of 5-fluorouracil administration, sublethal irradiation or bone marrow transplantation. SPECIFIC AIM 2 will investigate Trib'3 molecular action mechanisms, including regulation of Erk1,2 and Akt signaling, and action as a putative E3 ubiquitin ligase adaptor. In this aim I will study the effecs of inhibition of Erk1,2 and Akt in Trib3-KO and WT primary erythroid progenitor cells. I then will use co-immunoprecipitation and liquid chromatography tandem mass spectrometry methods to identify Trib3 targets. Findings will provide novel insights into Trib3's cellular and molecular action mechanisms in clinically relevant stress erythropoiesis models and may point to new candidate targets for anemia treatment. Importantly, I (with my mentor) have designed a detailed training program to advance scientific discoveries and provide strong career development opportunities. Included are collaborations with investigators at MMCRI and nationally, emersion in national meetings and workshops, bi- weekly, full institute, data reviews, training with expert core facility staff, and constructive bi-annual progress reviews. This trainin plan is designed to advance impacting first author papers and expertise as a new independent investigator.